The effects of temperature, salinity, and the carbonate system on Mg/Ca in Globigerinoides ruber (white) : a global sediment trap calibration
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The Mg/Ca of planktic foraminifera Globigerinoides ruber (white) is a widely applied proxy for tropical and sub-tropical sea-surface temperature. The accuracy with which temperature can be reconstructed depends on how accurately relationships between Mg/Ca and temperature and the multiple secondary controls on Mg/Ca are known; however, these relationships remain poorly quantified under oceanic conditions. Here, we present new calibrations based on 440 sediment trap/plankton tow samples from the Atlantic, Pacific and Indian Oceans, including 130 new samples from the Bay of Bengal/Arabian Sea and the tropical Atlantic Ocean. Our results indicate temperature, salinity and the carbonate system all significantly influence Mg/Ca in G. ruber (white). We propose two calibration models: The first model assumes pH is the controlling carbonate system parameter. In this model, Mg/Ca has a temperature sensitivity of 6.0±0.8%/°C (2σ), a salinity sensitivity of 3.3±2.2%/PSU and a pH sensitivity of −8.3±7.7%/0.1 pH units; The second model assumes carbonate ion concentration ([CO32−]) is the controlling carbonate system parameter. In this model, Mg/Ca has a temperature sensitivity of 6.7±0.8%/°C, a salinity sensitivity of 5.0±3.0%/PSU and a [CO32−] sensitivity of −0.24±0.11%/μmol kg−1. In both models, the temperature sensitivity is significantly lower than the widely-applied sensitivity of 9.0±0.6%/°C. Application of our new calibrations to down-core data from the Last Glacial Maximum, considering whole ocean changes in salinity and carbonate chemistry, indicate a cooling of 2.4±1.6°C in the tropical oceans if pH is the controlling parameter and 1.5±1.4°C if [CO32−] is the controlling parameter.
Gray , W R , Weldeab , S , Lea , D W , Rosenthal , Y , Gruber , N , Donner , B & Fischer , G 2018 , ' The effects of temperature, salinity, and the carbonate system on Mg/Ca in Globigerinoides ruber (white) : a global sediment trap calibration ' , Earth and Planetary Science Letters , vol. 482 , pp. 607-620 . https://doi.org/10.1016/j.epsl.2017.11.026
Earth and Planetary Science Letters
© 2017 Elsevier B.V. This work has been made available online in accordance with the publisher’s policies. This is the author created, accepted version manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at https://doi.org/10.1016/j.epsl.2017.11.026
DescriptionThis research was funded by NSF grant NSF-OCE 1260696 awarded to S. Weldeab and D.W. Lea.
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